For me, I'd be looking at the bigger picture. At age 11 do you really feel an invasive procedure is necessary? This is like putting an elderly human through a general. Also, does the cough bother him? Happen frequently? I wouldn't really want to put a cavalier that age thru a general anaesthesia and so forth unless the dog is clearly uncomfortable, there's a rea; problem and health risk, there's absolutely no other way to help him, and there's a clear idea of value gained compared to the likely lifespan for the dog.
I'd be wondering whether to just try treating for parasites if that is considered to be likely and isn't too difficult? I assume a cardio would have done an xray to check for heart enlargement as a cause, but if not, that would seem a more obvious starting point too.
I've always found a lot of specialists and vets will encourage procedures 'just to find out' or 'in case it helps as it could help' rather than considering whether the issue at hand poses any annoyance, pain or difficulty for the dog. Also they often will encourage quite invasive procedures in elderly animals. A friend's vet wanted her to do a very invasive procedurefor example on a quite elderly dog that recently passed away, and I just cound;t believe this had been recommended as the dog was already quite an old fellow -- what would be gained? My friend is so happy she didn;t actually do this as he'd hardly have recovered from the procedure before he passed away!
If I were in your shoes I'd sure not want to subject my dog to this and also spend $600 doing so, unless there were extremely compelling reasons. From your description it is hard to know if this is the case as I'm sure there are more involved details!
But if your vet wasn't concerned, and Misha seems fine otherwise, and it isn't heart related, some minor bronchitis wouldn't seem worth all this effort at least to me.
Just my own view!